Implantable medical devices, such as cardiac pacemakers, have become increasingly sophisticated. It is standard in the art to make such devices programmable, in the sense that the implanted device can receive telemetry signals from an external programmer which program its mode of operation, or operating parameters. Indeed, in modern cardiac systems there is extensive two-way communication between an implanted cardiac pacemaker and an external programmer device. Thus, data collected by the pacemaker and stored can be downloaded to the programmer, and programming instructions and other data can be transmitted from the programmer to the pacemaker. As another example of programming, see application Ser. No. 08/890,435, filed Jul. 9, 1997, and titled "Pacemaker System With Enhanced Programmable Modification Capacity", assigned to the same assignee as this invention, an implanted pacemaker can be designed to receive new software releases, each software release being downloaded into memory within the pacemaker to provide a functional modification of the operating characteristics of the pacemaker.
The technical circuitry required for both the programmer and the implanted device is well known in the art. The programmer generates telemetry signals, usually electromagnetic, which are received by an antenna within the implanted device. The antenna must be small enough to be accommodated efficiently within the housing of the device, but must also possess desired operating characteristics of sensitivity, directivity, etc. Since space within the implanted device is at a premium, it is essential that the antenna design be as efficient as possible. Modern pacemakers generally employ air core antennas for this purpose. The prior art discloses a number of different types of air core antennas. For example, air core coil antennas are wound on a separate coil carrier that is mounted on a circuit substrate. In another arrangement, the air core coil antenna is wound around a frame that is used for mounting the pulse generator assembly, comprising the battery and other circuitry, within the implantable pulse generator can. In another embodiment, ferrite core antennas are utilized, which may be mounted on or at the side of a hybrid circuit portion of the pulse generator.
Antenna designs currently in use for implanted medical devices generally are compromise designs which leave much room for improvement, either in the characteristics of the antenna as fabricated, or in the production process itself. What is needed in the art, particularly for implantable devices such as pacemakers where physical space is at a premium, but integrity of communication is critical, is an antenna design which allows efficient production steps adapted for an automated assembly line, as well as providing an antenna which does not separately take up space, and which is sensitive to linking with the programmer.